Arc suppression means



g- 2, 1966 R. w. MINCK ARC SUPPRESSION MEANS 2 SheetsSheet 1 Filed D60.30 1963 s K H m Mm mm a A 8 w m m R. WVMINCK 3,264,519

ARC SUPPRESSION MEANS Aug. 2, 1966 2 Sheets-Sheet 2 Filed Dec. $0, 1963ROBERT W. MIA/CK INVENTORf BY 9on5 re. a!

ATTOR/VAYJ United States Patent 3,264,519 ARC SUPPRESSION MEANS RobertW. Minck, Detroit, Mich, assignor to The Ford Motor (Iornpany, Bearborn,Mich, a corporation of Delaware Filed Dec. 30, 1963, Ser. No. 334,173 '7Claims. (Cl. 3152G6) This invention relates to means for protectingelectrical switching elements in current interrupters and moreparticularly it relates to such a means placed in circuit with theelectrical contact points or other switching element of an ignitionsystem for an internal combustion engine.

A typical way of preventing arcing between contact points of anelectrical switch when interrupting a current, particularly in aninductive circuit, is to connect a capacitor across the contact points.Upon opening of the contact points the capacitor provides, temporarily,an alternate current path thereby keeping the voltage across the contactpoints low during the period when the contact points are separating.This reduces arcing and contact electrode deterioration during theopening of the contact points.

In the conventional automotive ignition system, a capacitor is connectedacross the ignition contact breaker points. This capacitor is necessaryfor proper operation of the ignition system and to prevent contact wearat an extremely high rate. If a capacitor is not used, there isconsistent arcing between the contact breaker points and the associatedenergy loss prevents sufficient ignition voltage from building up. Withthe capacitor currently used in automotive ignition systems, arcing isgreatly reduced over the case where no capacitor is used, and theresultant small amount of arcing does not affect significantly thebuildup of proper ignition voltages. This arcing is still highlyundesirable, however, in that it gives rise to rate of contact wear muchhigher than that which would result with no arcing.

One proposed solution to this problem is to employ a larger capacitorthan the one currently used, and this would definitely reduce arcingduring contact opening. With a larger capacitor, however, a seriousproblem of arcing arises upon the closing of the contacts, since thelarge amount of charge on this larger capacitor would tend to create anarcing condition as the contacts close.

The present invention is directed toward the solution of contact arcingand to the protection of other switching elements in currentinterrupters and more particularly to the solution of this problem in aninternal combustion engine ignition system. In the present invention alarge capacitor may be connected across the ignition breaker points, ora switching transistor, if this is used, in the system. This capacitorwill be large enough to prevent any arcing when the breaker points open,or to prevent unduly high voltages from occurring across the transistorwhen the transistor is being switched from its conducting to itsnonconducting state. Discharge of the capacitor through the contactswhen the contacts are closing, or through the transistor when thetransistor is being switched from its nonconducting to its conduct-ingstate, is prevented by connecting a zener diode between the ignitionbreaker points or transistor and the capacitor. This zener diode ispoled so that the capacitor may charge when the ignition breakercontacts are opening, or the transistor is being switched to itsnonconducting state. The direction of the charging current in this caseis in the forward conduction direction of the zener diode. The zenerdiode is selected to have a zener or reverse breakdown voltageapproximately equal to the terminal voltage of the source of electricalenergy or storage battery connected to energize the ignition system.

It is well known that when the ignition breaker points open or thetransistor is switched to its nonconducting state, that the system ineffect becomes an LC oscillatory circuit in which large voltage orenergy oscillations occur. For example, with a twelve volt battery thevoltage across the primary winding of the ignition coil may rise to 250volts in an effort to maintain the current flow through the circuit asthe ignition breaker contact points open or the transistor is switchedto its nonconducting state. These oscillations have both negative andpositive voltage amplitudes with a frequency determined by theinductance and capacitance of the circuit. With the zener diodepositioned in the circuit, having a reverse breakdown or zener voltagesubstantially equal or slightly greater than the terminal voltage of thestorage battery, substantially all the large amount of energy stored inthe capacitor may be returned to the circuit during the oppositepolarity swing of the oscillations. This is true since the zener diodewill break down and conduct in the reverse direction when the reversevoltage across it exceeds the zener voltage. Thus for all reversevoltages in excess of the zener voltage the circuit is free tooscillate.

When the oscillations die out the capacitor is charged to the batteryvoltage. The zener diode eifectively isolates the ignition breakerpoints or transistor from the capacitor when the breaker points close,or the transistor is switched to its conducting state, so that thecapacitor cannot discharge through the ignition breaker points or thetransistor to cause destructive arcing or energy dissipation. Means areprovided, of course, to allow the charge on the capacitor to drain ofislowly during the time the ignition points are closed, or the transistoris in its conducting state, so that the capacitor is again dischargedwhen the breaker points open or the transistor is switched to itsnonconducting state.

Thus, the use of the zener diode eiiectively isolates the capacitor fromthe ignition breaker points or transistor when the ignitionbreaker'points are closing or the transistor is being switched to itsnonconducting state. At the same time, however, it permits theoscillations in the ignition system and permits this oscillatory energyto be transferred to the secondary winding of the ignition coil and tothe spark plugs of the internal combustion engine.

With the use of the zener diode, a much larger arc suppression capacitorthan is currently being used may be employed. This arc suppression maybe selected to be of a size to prevent arcing when the ignition breakerpoints are being opened or if a transistor is used, to preventdestructive energy dissipation in the transistor when the transistor isbeing switched to its nonconducting state. The ignition system of thepresent invention will furnish proper oscillatory energy to the sparkplugs of the ignition system and destructive arcing or energydissipation will be prevented in the switching element, contact pointsor transistor, when the switching element is switched to its conductingstate.

It should be noted that although the invention has been developedspecificaly for ignition systems, that it can be used equally well inother systems in which protection of con-tact points or of transistorsis required. An object of the invention is the provision of means forpreventing destructively high voltages from being applied to a switchingelement during opening and clos ing of the switching element.

Another object of the invention is the provision of a means to reducearcing in the contact points of an electrical switching circuit.

A further object is the provision of an ignition systern for an internalcombustion engine in which sub stantially all of the oscillatory energyin the system is delivered to the spark plugs of the system and theswitching element that switches the current in the primary circuit of anignition coil is adequately protected both upon opening and closing ofthis switching element.

Another object of the invention is the provision of a means foreliminating arcing in the electricl contact points of the ignitionsystem for an internal combustion engine and for simultaneouslydelivering substantially all of the oscillatory energy in the primarycircuit of the ignition coil to the spark plugs of the system.

Other objects and attendant advantages of the present invention willbecome fully apparent as the specification is considered in connectionwith the attached drawings in which:

FIGURE 1 is a circuit diagram of an ignition system for an internalcombustion engine employing the present invention; 7

. FIGURE 2 is a modification of the invention as applied to the ignitionsystem of FIGURE 1;

FIGURE 3 is a circuit diagram of a transistorized ignition system for aninternal combustion engine employing the present invention, and

FIGURE 4 is a modification of the invention as applied to the ignitionsystem of FIGURE 3.

views thereof, there is shown in FIGURE 1 one embodiment of the presentinvention as applied to a conventional internal combustion engineignition system in which a source of electrical energy in the form ofstorage battery has one electrode 11 connected to ground through a lead12 and the other electrode 13 connected to ignition switch 14 through alead 15. The ignition switch 14 is connected through a lead 16 to .theprimary winding 17 of an igintion coil 18. The terminal of the ignitioncoil opposite the lead 16 is connected to a junction 19 through a lead21. The junction 19 is connected through a lead 22 to one contact orelectrode 23 of Va set of. distributor contact breaker points 24. The

other contact or electrode 25 of this set of distributor contact breakerpoints is mounted on a movable arm 26 and this movable arm is connectedto a ground lead or wire 27 through a lead 28.

A zener diode 31 is connected to both the primary winding 17 and thecontact 23 of distributor contact breaker points 24 by having its anode32 connected to the junction 19. The cathode '33 of the zener diodeother terminal connected to a rotating arm 45 of distri-butor 46 througha lead 47. The distributor is of conventional construction and includesthe usual rotor cap in which spaced electrical contacts 51 through 56are connected to spark plugs 57 .through 62 by means of leads 63 through68 respectively. As is conventional in distributor construction, therotating arm 45 is rotated (in synchronism with a contact breaker pointinterrupting means, preferably in the form of a cam 71, by the powerdeveloped by the internal combustion engine that employs this ignitionsystem.

As is conventional in such an ignition system, the distributor con-tactbreaker points 24 are closed when the rotating arm 45 is out of contactwith the contacts 51 through '56. At this time, assuming the ignitionswitch 14 to be closed, current builds up in the primary winding 17 ofignition coil 18 creating a rising magnetic field. When the rotating arm45 reaches one of the contacts 51 through '56, the breaker points 24 areopened so that the contacts or electrodes 23 and 25 separate. Thisinterrupts the current flow through the primary winding 17 of theignition coil 18 and induces an electrical voltage of high magnitude inthe secondary winding 43. This voltage is applied through the circuitpreviously described including the lead 47, the rotating arm 45,electrical contacts 51 through 56, and leads 63 through 68, tosequentially fire the spark plugs 57 through 62. a

When thevdistr-ibutor contact breaker points 24 open,

the voltage across the primary winding of the ignition.

' be readily appreciated that when the distributor contact breakerpoints open, that the primary circuit is in effect a series LC circuitbecause of the inductance of the primary winding 17 and the capacitanceof the capacitor 35. This circuit will oscillate with an amplitude andfrequency determined by the circuit parameters and, as stated, theamplitude may exceed 250 volts. These oscillations will gradually dieout as determined by the damping ratio of the circuit.

The zener diode 31 may be selected so that ithas a zener or reversebreakdown voitage approximately equal to the terminal voltage of thestorage battery 10, and the zener voltage should be greater, in anycase,than the voltage on the capacitor 35, when distributor contact breakerpoints 24 commence to close. For example, if the terminal voltage of thestorage battery 10 is twelve volts, the zener diode may be selected tohave a reverse breakdown or zener voltage of thirteen volts.

The high voltage amplitude oscillations alternately apply a reversevoltage or back voltage and a forward voltage on the zener diode 31. Allof the energy of that portion of the oscillations that apply a forwardvoltage to the zener diode 31 may pass through the zener diode 31. Thatportion of the energy that is above the zener voltage may pass throughthe zener diode 31 in the reverse or back direction because the zenerdiode breaks down at this voltage. Thus only that energy that is belowthe zener voltage of the diode and of a polarity to apply a reversevoltage to the zener diode 31 is lost from the oscillatory energy of theprimary circuit of the ignition system.

The capacitor 35 may be selected to be large enough to delay a highvoltage rise across the distributor contact breaker points 24 as thebreaker contact points 24 open. The voltage rise is delayed until thecontacts or electrodes 23 and 25 are separated sufliciently so thatareing cannot occur at the highest voltages induced in the primaryWinding 17 of the ignition coil. At this time, of course, the capacitoris effectively connected across the contacts or electrodes 23 and 25since the zener diode a conventional linear capacitor or a saturablecapacitor of the type that will return to substantially an unchargedcondition when the voltage is removed from it.

After the distributor contact breaker points 24 open,

the oscillations described above and the action of the zener diode 31described above provides a proper oscillatory ignitionvoltage or energyto the spark plugs 57" through 62.

When these oscillations finally die out it can be un-- derstood that thecapacitor 35 is charged to the terminal voltage of the battery 10. Whenthe electrodes 23 and of the distributor contact breaker points 24commence to close, after being opened, the zener diode 31 prevents thecapacitor from discharging through the contacts or electrodes 23 and 25since the zener voltage or reverse breakdown voltage of the zener diode31 is equal to or slightly greater than the terminal voltage of thestorage battery 16 or the voltage to which the capacitor 35 is charged.Thus the energy stored in the large capacitor 35 is not dischargedthrough these contact breaker points 24 but is discharged through theresistor 38 and the rate of discharge is determined by the time constantof this circuit. It is necessary, of course, that the capacitor 35 bedischarged prior to the time that the ignition contact breaker points 24again commence to open.

In FIGURE 2 the resistor has been eliminated and in this case the use ofthe zener diode 31 having a low back resistance is contemplated. It iswell known that in ignition systems, the contact breaker points areclosed for a much longer period of time than they are open and the lowback resistance of the zener diode 31 will permit the capacitor 35 todischarge back through the zener diode and through the closed contactelectrodes 23 and 25 of the contact breaker points 24. The resistance ofthe diode 31, however, will be sufiiciently high so that the capacitor35 cannot discharge rapidly through the contact breaker points 24- asthey close. Rather, the capacitor can discharge slowly through the zenerdiode 31 and the contact breaker points 24 when they are closed. Thusthe contact breaker points 24 will have very little current flow throughthem to cause arcing upon closing. The circuit of FIGURE 2 implies thata very inexpensive zener diode can be employed since a zener diode witha reasonably low back resistance is very much less expensive than onewith a very high back resistance. The same type of zener diode, ofcourse, may be employed in FIGURE 1, if desired, with the additionalresistor 38 being provided for a more rapid discharge of the capacitor35.

In FIGURE 3, the invention is applied to a transistorized ignitionsystem in which a transistor 81 is employed to control current flow inthe primary winding 17 of the ignition coil 18. As shown, the transistor81 is of the NPN type in which a collector S2 is connected to thejunction 19 through a lead 83 and the emitter 84 is connected to groundlead or wire 27 through a lea-d 85. Thus the output circuit of thetransistor 81, comprising the collector 82 and the emitter 84, isconnecied in circuit or in series with the source of electrical energyor battery 10 and the primary winding 17 of the ignition coil 18.

The base 86 of the transistor 81 is connected to the electrode 13 of thebattery 1% through a resistor 87 and a set of contact breaker points 88,the lead 16, ignition switch 14 and lead 15. As is conventional intransistor circuits, a biasing resistor 89 is connected between the base86 and the emitter 84. This is accomplished by connecting the resistor8Q to the base and to the ground lead or wire 27.

In operation of this circuit, the cam 71 operates in synchronism withthe rotating arm as in the embodiment of the invention shown inFIGURE 1. When the set of contact breaker points 88 is closed, thetransistor 81 is in its conducting state since the base 86 is properlybiased with respect to the emitter 84 and current may flow through thebase circuit. When the contact breaker points 88 open, the transistor 81is switched from its conducting to its nonconducting state since thebase circuit is opened by the opening of the con-tact breaker points 88.At this time, the capacitor 35 charges through the zener diode 31providing a temporary alternate current path for the current that waspreviously flowing through the transistor when the transistor was in itsconducting state and delaying the onset of the high voltage oscillationspreviously described. This prevents a high voltage rise across thetransistor when it is in its switching state, and this prevents highenergy dissipation on the transistor when it is being switched from itsconductng to its nonconducting state. The high oscillatory voltages canthen occur without damage to the transistor 81 because it issubstantially nonconducting and very little energy can be dissipated init. The zener diode 31 in this circuit would be of the same type andhave the same rating as the one employed with the circuit shown inFIGURE 1. That is, the zener or reverse breakdown voltage of the zenerdiode 31 will be approximately equal to or slightly greater than theterminal voltage of the battery 10 or eqaul to or slightly greater thanthe voltage on the capacitor 35 when the transistor 81 is switched toits conducting state, and the zener diode will act in the same way topermit oscillations in the circuit including the primary winding 17 ofthe ignition coil and the capacitor 35, thereby permitting oscillatoryenergy to be applied to the spark plugs 57 through 62 via thedistributor 46. This circuit implies that an inexpensive transistor maybe employed in the transistorized ignition system since the largevoltages induced in the primary winding 17 are delayed until thetransistor is completely switched from its conducting to itsnonconducting state and the capacitor 35 cannot discharge through thetransistor when the transistor is switched from its nonconducting to itsconducting state.

When the contact breaker points 88 again close, the transistor 31 willbe switched from its nonconducting to its conducting state and the zenerdiode 31 will prevent the capacitor 35 from discharging back through thetransistor 31 and thus prevent high energy dissipation in the transistor81 when the transistor 81 is switched from its nonconducting to itsconducting state.

The resistor 33 provides a path for discharging the capacitor 35 as wasthe case in the embodiment of the in vention shown in FIGURE 1. In otherrespects, the embodiment of the invention shown in FIGURE 3 operates inthe same manner as the embodiment of the invention shown in FIGURE '1with the contact breaker points 83 opening when the rotating arm 45 ofthe distributor 46 is in contact with one of the electrical contacts 51through 56.

The embodiment of the invention shown in FIGURE 4 is similar to thatshown in FIGURE 2 as applied to the transistorized ignition system shownin FIGURE 3. In FIGURE 4, a low back resistance zener diode 31 maybeemployed and it functions in the same manner as the low back resistancezener diode disclosed in FIGURE 2.

It can be appreciated that in the embodiment of the invention shown inFIGURES 3 and 4, the contact breaker points 88 switch only low basecurrent of the transistor 81 and, therefore, are not subject to a largeamount of arcing and deterioration. Also, it should be appreciated thatany pulse generator for generating pulses to turn the transistor 31 onand off to switch it alternately from its conducting to itsnonconducting state may be employed in place of the set of ignitioncontact breaker points 88.

Thus the present invention provides a means for protecting a switchingelement in a current interrupting circuit during both the opening andthe closing of the switching element. It is particularly useful in anignition system for an internal combustion engine in which it preventsarcing on both the opening and closing of a set of ignition contactbreaker points. It may also be employed in an ignition system for aninternal combustion engine employing a transistor and it prevents highvoltages from being applied across the transistor and thus prevents highenergy dissipation in the transistor when it is being switched fromeither its conducting to its nonconducting state or from itsnonconducting to its conducting state. While providing this protectionfor the switching element in an ignition system, it also permits highlydesirable oscillatory energy to be delivered to the spark plugs of theignition system. This is brought about by the use of the zener diode inthe primary circuit of the ignition system that properly protects theignition contact breaker points or transistor while at the same timepermitting oscillatory transfers of energy in the primary circuit of theignition system at all voltages above the zener or reverse breakdownvoltage of the zener diode.

It is to be understood that this invention is not to be limited to theexact construction shown and described but that various changes andmodifications may be made without departing from the spirit and scope ofthe invention as defined in the appended claims. a

I claim:

1. In an ignition system for an internal combustion engine thecombination comprising, a plurality of spark plugs, an ignition coilincluding a primary winding and a secondary winding, a distributor forsequentially connecting said secondary winding with said spark plugs, asource of electrical energy and a set of breaker contacts connected inseries with said primary winding, means operated by said distributor forperiodically opening said set of breaker points in synchronism with theconnection of said secondary winding with said spark plugs, a capacitorand a zener diode connectedin series circuit, said series circuitconnected across said set of breaker contacts, said zener diode beingpoled to permit said capacitor to charge through said zener diodewhen'said breaker con tacts are opened and to prevent rapid discharge ofsaid capacitor through said breaker contacts when said breaker contactsclose, said zener diode having a zener breakdown voltage at least equalto the voltage on said capacitor just prior to the time said breakercontacts commence to close.

2. In an ignition system for. an internal combustion engine thecombination comprising, a spark plug, an ignition coil including aprimary and a secondary winding, said secondary winding beingconnectable to said spark plug, a source of electrical energy connectedto said primary winding of said ignition coil, a set of contactsconnected in circuit with said source of electrical energy and saidprimary winding of said ignition coil for controlling the energizationof said primary winding, means operable by the internal combustionengine for opening and closing said set of contacts and for connectingsaid spark plug to said secondary winding, a capacitor and a zener diodeconnected in series circuit, said series circuit connected across saidset of contacts, said zener diode being poled to [permit said capacitorto charge through said zener diode when said set of contacts opens andfor preventing said capacitor from discharging rapidly through said setof contacts when said set of contacts close, said zener diode having abreakdown voltage at least equal to the terminal voltage of said sourceof electrical energy whereby a majority of the energy stored in saidcapacitor is returned to said primary winding and said source ofelectrical energy after said set of contacts opens.

3. An electrical circuit, a source of electrical energy, an inductivecircuit element, a switching element connected in series with saidsource of electrical energy and said inductive circuit element, meanscoupled to said switching element for switching said switching elementbetween its conducting and nonconducting states, a series circuitincluding a capacitor and a zener diode connected across said switchingelement, said zener diode being poled to permit said capacitor to chargewhen said switching element is switched to its nonconducting state byforward current flow through said zener diode and to prevent rapiddischarge of said capacitor through said switching element whensaidswitching element is in its conducting state, said zener diode having abreakdown voltage at least equal to the voltage on said capacitor whensaid switching element is switched from its nonconducting to itsconducting state.

4. In an ignition system [for an internal combustion engine thecombination comprising, a spark plug, an ignition coil'including aprimary and a secondary winding, said 8 secondary winding beingconnectable to said spark plu a source of electrical energy, atransistor having an output circuit electrode connected in circuit tocontrol the ener gization of said primary winding of said ignition coilfrom said source of electrical energy, said transistor having an inputcircuit, means operable by said internal combustion engine and coupledto said input circuit for switching said transistor alternately betweena conducting and a nonconducting state, said last mentioned meansincluding means for alternately connecting and disconnecting saidsecondary winding of said ignition coil to and from said spark plug insynchronism with the switching of said transistor, a capacitor and azener diode connected in series circuit, said series circuit connectedacross the output electrodes of said transistor, said zener diodeconnected series with said primary winding, said zener diode being poledto permit said capacitor to charge by forward current flow through saidzener diode when said transistor is switched from its conducting to itsnonconducting state and to prevent said capacitor from dischangingrapidly through said transistor when said transistor is switched rfromits nonconducting to its conducting state, said zener diode having azener voltage at least equal to the voltage on said capacitor when saidtransistor is switched to its conducting state.

5. In an ignition system for an internal combustion engine, a sparkplug, an ignition coil including a primary winding and a secondarywinding, an electrical storage battery, and a switching elementconnected in series with said primary winding of said ignition co-il,means operable by said internal combustion engine for switching saidswitching element periodically between conducting and nonconductingstates, a capacitor and a zener diode connected in series circuit, saidseries circuit connected across said switching element and in serieswith said primary winding of said ignition coil, said capacitor and saidprimary winding of said ignition forming an inductive capacitiveoscillatory circuit producing oscillating voltages across said primarywinding having an initial amplitude at least several times greater thanthe terminal voltage of said source of electrical energy, said zenerdiode having a reverse breakdown voltage at least equal to the voltageon said capacitor when said switching element is switched to itsconduct-ing state, said zener diode being poled in a direction to permitcurrent flow through said zener diode in a forward direction to chargesaid capacitor whereby a majority of the oscillatory energy may passthrough said zener diode between said primary winding and said capacitorafter said switching element is switched from the conducting to thenonconducting state and said zener diode prevents said capacitor fromdischarging through said switching element when said switching elementis switched to its conducting state, and means connected to saidcapacitor for permitting said capacitor to discharge.

6. In an ignition system for an internal combustion engine, a sparkplug, an ignition coil including aprimary winding and a secondarywinding, an electrical storage battery, and a set of contacts connectedin series with said primary winding of said ignition coil, meansoperable by said internal combustion engine for periodically opening andclosing said set of contacts, a capacitor and a zener diode connected inseries circuit, said series circuit connected across said set ofcontacts and in series with said primary winding of said ignition coil,said capacitor and said primary winding of said ignition coil forming aninductive capacitive oscillatory circuit producing oscillating voltagesacross said primary winding having an initial amplitude at least severaltimes greater than the terminal voltage of said source of electricalenergy when said set of contacts is opened, said capacitor beingsufficiently large to prevent arcing across said set of contacts as saidset of contacts open, said zener diode having a reverse breakdownvoltage substantially equal to the terminal voltage of said electricalstorage battery and poled in a direction to permit current flow throughsaid zener diode in a forward direction to charge said capacitor wherebya majority of the oscillatory energy may pass through said zener diodebetween said primary winding and said capacitor during the period whensaid set of contacts is opened and said zener diode prevents saidcapacitor from discharging through said set of contacts when said set ofcontacts is closed, and means connected to said capacitor for permittingsaid capacitor to discharge.

7. In an ignition system for an internal combustion engine, a sparkplug, an ignition coil including a primary winding and a secondarywinding, an electrical storage battery, and a transistor connected inseries with said primary winding of said ignition coil, means operableby said internal combustion engine for switching said transistorperiodically between conducting and nonconducting states, a capacitorand a zener diode connected in series circuit, said series circuitconnected across said switching element and in series with said primarywinding of said ignition coil, said capacitor and said primary windingof said ignition forming an inductive-capacitive oscillatory circuitproducing oscillating voltages across said primary winding having aninitial amplitude at least several times greater than the terminalvoltage of said source of electrical energy when said transistor isswitched to its nonconducting state, said capacitor being sufficientlylarge to prevent damage to said transistor as said transistor is beingswitched from its conducting to its nonconducting state, said zenerdiode having a reverse breakdown voltage substantially equal to theterminal voltage of said electrical storage battery and poled in adirection to permit current flow through said zener diode in a forwarddirection to charge said capacitor, whereby a majority of theoscillatory energy may pass through said zener diode between saidprimary winding and said capacitor when said transistor is switched fromthe conducting to the nonconducting state and said zener diode preventssaid capacitor from discharging through said transistor when saidtransistor is switched to its conducting state, and means connected tosaid capacitor for permitting said capacitor to discharge.

References Cited by the Examiner UNITED STATES PATENTS 6/1960 Kerr315209 7/1962 Martin 315209 OTHER REFERENCES 25 JOHN W. HUCKERT, PrimaryExaminer.

D, O. KRAFT, Assistant Examiner,

3. AN ELECTRICAL CIRCUIT, A SOURCE OF ELECTRICAL ENERGY, AN INDUCTIVECIRCUIT ELEMENT, A SWITCHING ELEMENT CONNECTED IN SERIES WITH SAIDSOURCE OF ELECTRICAL ENERGY AND SAID INDUCTIVE CIRCUIT ELEMENT, MEANSCOUPLED TO SAID SWITCHING ELEMENT FOR SWITCHING SAID SWITCHING ELEMENTBETWEEN ITS CONDUCTING AND NONCONDUCTING STATES, A SERIES CIRCUITINCLUDING A CAPACITOR AND A ZENER DIODE CONNECTED ACROSS SAID SWITCHINGELEMENT, SAID ZENER DIODE BEING POLED TO PERMIT SAID CAPACITOR TO CHARGEWHEN SAID SWITCHING ELEMENT IS SWITCHED TO ITS NONCONDUCTING STATE BYFORWARD CURRENT FLOW THROUGH SAID ZENER DIODE AND TO PREVENT RAPIDDISCHARGE OF SAID CAPACITOR THROUGH SAID SWITCHING ELEMENT WHEN SAIDSWITCHING ELEMENT IS IN ITS CONDUCTING STATE, SAID ZENER DIODE HAVING ABREAKDOWN VOLTAGE AT LEAST EQUAL TO THE VOLTAGE ON SAID CAPACITOR WHENSAID SWITCHING ELEMENT IS SWITCHED FROM ITS NONCONDUCTING TO ITSCONDUCTING STATE.